Steam Power Generator.pdf

TABLE OF CONTENTS CHAPTER NO

CHAPTER TITLE

PAGE NO

CHAPTER-1

Literature review

07

CHAPTER-2

Introduction

10

Components of pressure vessels

12

2.21

Shell

12

2.22

Head

12

2.23

Nozzle

13

2.24

Support

13

2.3

Mount storage vessel

14

2.4

History of pressure vessel

15

2.4.1

Classification of boilers

17

2.4.2

High pressure vessel

18

2.4.4

Type of failures

19

2.4.5

Types

20

2.4.6

Thermal stress

22

Fatigue analysis

22

2.5.1

Stress

23

2.5.2

Type of stress

24

2.2

2.5

1

2.5.3

Primary general stress

25

2.5.4

Pressure stress

26

2.5.5

Secondary stress

26

Failure in pressure vessels

27

Codes and standards

29

Materials of constructions

30

Materials of constructions

31

Material property summary

32

Material selection for pressure vessel

33

2.6 Chapter-3

3.1

construction 3.2

General material selection process

34

3.3

Material used for pressure vessels

34

1

Q235-A

34

2

20g

35

3

16MnR

35

4

The material for low temperature vessel

36

Steel for high temperature vessel

36

Design of multilayer high pressure vessel

37

4.1

Design objectives

38

4.2

Design consideration

39

3.4 Chapter-4

2

4.3

Design data of vessel

40

4.4

Design criteria

41

Minimum shell/head thickness

42

Factor considered for designing pressure

43

4.4.1 Chapter-5

vessel 5.1

Vessel sizing

43

5.2

Vessel end closure

43

5.3

Pressure

44

5.3.1

Operating pressure

44

5.3.2

Design pressure

45

5.3.3

Test pressure

47

5.3.4

Corrosion allowance

48

5.5

Calculation

49

5.6

Design procedure and calculation

50

5.6.1

Circumferential or hoop stress

51

5.6.2

Longitudinal stress

52

Design of shell due to internal pressure

52

5.7.1

Rule

52

5.7.2

Design of elliptical head

52

Design calculation

53

5.7

5.8

3

5.8.1

Thickness of cylinder

53

5.8.2

Design of man hole

54

5.8.3

Design calculation summary

54

Advantages

55

Conclusion

56

Reference

57

4

Figure No

Figure Name

Page No

Codes and standards

29

Materials of constructions Case-2

30 31

Material of constructions Material property summary

32

Design data of vessel

40

Design calculation summary

54

5

DESIGN AND FABRICATION OF STEAM POWER PLANT

ABSTRACT

The main objective of this paper is to design and fabrication of steam power plant. analysis of multilayer high pressure vessels features of multilayered high pressure vessels, their advantages over mono block vessel are discussed. Various parameters of Multilayer Pressure vessels are designed and checked according to the principles specified in American Society of Mechanical Engineers (A.S.M.E). A boiler is a closed vessel in which water or other fluid is heated. The fluid does not necessarily boil. ("furnace" is normally used if the purpose is not actually to boil the fluid.) The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.

6

CHAPTER:1 LITERATURE REVIEW High-pressure vessels, such as ammonia converters, urea reactors and supercritical fluid extractors, etc., are widely used in chemical, oil refining, energy industries, and so on. Such vessels are key equipments in various processes industries and have potential hazards. Much attention has been paid to using them safely and to lowering their costs, with great progress being made in the last century. For example, Analysis of Pressure Vessel junction

by

the

Finite

element

Method

written

by

Mahadeva

Sivaramakrishna Iyer not only tells the use of method to solve such high tension zone problems but also gives a way to predict results for stresses and optimize the design [1], Finite element analysis of Pressure vessel by David Heckman also tells the use of computer programs instead of hand calculations for analyzing the high stress area’s and different end connections [2].The different types of stresses and modeling of pressure vessel joints are also depicted in ASME code in section “Design by analysis” [3]. the use of hemispherical end in pressure vessels is the most economical and common use which can be seen in India and other developing countries. Although with the recent trends in Mechanical 7

engineering with the use of Finite element software’s the sheet thicknesses are validated for different end connections and for cylinder shell itself. As per the conventional theory of mechanics of materials stated by S Timoshenko, the required thickness of hemispherical end is one-half the thickness of the shell to result in equivalent stresses in the cylinder

[4] Adali et al. (1995) gave another method on the optimization of multi-layered composite pressure vessels using an exact elasticity solution. A three dimensional theory for anisotropic thick composite cylinders subjected to axis symmetrical loading conditions was derived. The three dimensional interactive Tsai-Wu failure criterion was employed to predict the maximum burst pressure. The optimization of pressure vessels show that the stacking sequence can be employed effectively to maximum burst pressure. However Adali’s results were not compared with experimental testing and the stiffness degradation was not considered during analysis. [5] The effect of surface cracks on strength has been investigated theoretically and experimentally for glass/epoxy filament wound pipes, by Tarakçioglu et al. (2000). They were investigated theoretically and experimentally the effect of surface cracks on strength in glass/epoxy filament wound pipes which were exposed to open ended internal pressure. 8

[6]

Mirza etal. (2001) investigated

the composite vessels under concentrated moments applied at discrete lug positions by finite element method. Jacquemin andVautrin (2002) examined the moisture concentration and the hydro thermal internal stress fields for evaluating the durability of thick composite pipes submitted to cyclic environmental condition. Sun et al. (1999) calculated the stresses and bursting pressure of filament wound solid-rocket motor cases which are a kind of composite pressure vessel; maximum stress failure criteria and stiffness-degradation model The present research focuses on: a. Determination of first failure pressures of pressure vessels by using a finite element method b. Optimization of composite pressure vessels c. Comparison of filament winding angles of composite pressure vessels d. Comparison of theoretical results with experimental

9

CHAPTER: 2 INTRODUCTION

2. INTRODUCTION

In Process Industries, like chemical and petroleum industries design have recognized the limitations involved for confining large volumes of high internal pressures in single wall cylindrical metallic vessels. In process engineering as the pressure of the operating fluid increases, increment in the thickness of the vessel intended to hold that fluid is an automatic choice. The increment in the thickness beyond a certain value not only possesses fabrication difficulties but also demands stronger material for the vessel construction. The media which a pressure vessel contains produce critical changes to the physical properties of the vessel material during service. One of these that is often encountered is hydrogen, which under the action of high pressure and / or high temperature produces two effects: (1) A diffusion into the metal as atomic hydrogen and a process of recombining to its molecular form within the metal, thereby creating extremely high pressures with resulting surface bulging, and (2) a mechanical decarburizing, and reducing

10

effect on sulfides or oxides present in the steel creating a brittleness and resultant cracking under high stress. Multilayer Pressure Vessels have extended the art of pressure vessel construction and presented the process designer with a reliable piece of equipment useful in a wide range of operating conditions for the problems generated by the storage of hydrogen and hydrogenation processes the term pressure vessel referred to those reservoirs or containers, which are subjected to internal or external pressures. The pressure vessels are used to store fluids under pressure. The fluid being stored may undergo a change of state inside the pressure vessels as in case of steam boilers or it may combine with other reagents as in chemical plants. Pressure vessels find wide applications in thermal and nuclear power plants, process and chemical industries, in space and ocean depths, and in water, steam, gas and air supply system in industries. The material of a pressure vessel may be brittle such as cast iron, or ductile such as mild steel.

11

2.1 INTRODUCTION TO PRESSURE VESELS

Pressure vessel is a closed container containing fluid under pressure (internal or external) more than the atmospheric pressure used for channeling and storing fluids and for performing various unit operations.

2.2 COMPONENTS OF PRESSURE VESSELS 2.2.1 SHELL The shell is the primary component that contains the pressure. Pressure vessel shells are welded together to form a structure that has a common rotational axis. Most pressure vessel shells are cylindrical, spherical and conical in shape.

2.2.2 HEAD All pressure vessel shells must be closed at the ends by heads (or another shell section). Heads are typically curved rather than flat. Curved configurations are stronger and allow the heads to be thinner, lighter, and less expensive than flat heads. Heads can also be used inside a vessel.

12

2.2.3 NOZZLE A nozzle is a cylindrical component that penetrates the shell or heads of a pressure vessel. The nozzle ends are usually flanged to allow for the necessary connections and to permit easy disassembly for maintenance or access. Nozzles are used for the following applications

 Attach piping for flow into or out of the vessel.  Attach instrument connections, (e.g., level gauges, thermo wells, or pressure gauges).  Provide access to the vessel interior at many ways.

2.2.4 SUPPORT

The type of support that is used depends primarily on the size and orientation of the pressure vessel. In all cases, the pressure vessel support must be adequate for the applied weight, wind, and earthquake loads. Calculated base loads are used to design of anchorage and foundation for the pressure vessels.

13

2.3 MOUNDED STORAGE VESSEL Comprises the storage of pressurized gases at ambient temperatures in horizontal cylindrical vessels placed near ground level and covered with suitable backfill. Several vessels may be located side by side in one mound. The decision for the earth covered type of installation is mainly justified by the safety advantages in respect to external influence on the vessel; such has high temperature in case of fire and dynamic pressure from near by explosion. The design procedure of the mounded storage vessel conforms to ASME-Boiler and Pressure vessel code, section VIII pressure vessels – Division II .The various stresses (due to pressure, seismic, mound and dead loads) on mounded storage vessel are calculated. Stress analysis of mounded storage vessel is done with the help of the FEA (Finite element analysis) package ANSYS. Induced stresses obtained from manual calculations using fundamental formulae and induced stresses obtained from FEA using ANSYS were compared

14

2.4 HISTORY OF PRESSURE VESSELS:

Pressure vessels are a group of critical equipments of different types of construction used in modern industries for various operations like storage, process etc. of various fluids. These equipments can be  Atmospheric Storage Tanks

 Pressurized Tanks

 Process columns and Vertical Pressure Vessels

 Horizontal Pressure Vessels

 Heat Exchangers

 Process Heaters

Boilers Throughout the world the use of process equipment has expanded considerably. In petroleum industry, pressure vessels are used at all stages of processing oil. At the beginning of cycle, they are used to store 15

crude oil. Much different types of these pressure vessels, process the crude oil into oil and gasoline for the customer. The use of pressure vessels in chemical industries is equally extensive. Pressure vessels are made in all sizes and shapes. The smaller one may be no longer than a fraction of an inch in diameter; whereas large pressure vessels may be of dia 150ft. or more in India .Some are buried in ground or deep in oceans, most are positioned on ground or supported on platform and some are found as storage tanks and hydraulic units in aircrafts.

The internal pressure to which process equipment is designed is varied as size and shape. The usual range of pressure for mono block construction is about15 psi to 5000 psi. Although there are many vessels designed for pressure below and above that range .The ASME boiler and pressure vessel code section VIII Div.II, specify a range of internal pressure from 15 psi at bottom to no upper limit. However at an internal pressure above 3000 psi.

16

2.4.1 CLASSIFICATION OF BOILERS

Unfired Cylindrical Pressure Vessels (Classification Based on IS 28251969)

a) Class 1: Vessels that are to contain lethal or toxic substances. Vessels designed for the operation below -20 C and Vessels intended for any other operation not stipulated in the code. b) Class 2: Vessels which do not fall in the scope of clas1 and class 3 are to be termed as class2 vessels. The maximum thickness of shell is limited to 38 mm. c) Class 3: There are vessels for relatively light duties having plate thickness not in excess of 16 mm, and they are built for working pressures at temperatures not exceeding 250 c and unfired .class3 vessels are not recommended for services at temperature below 0c.

17

2.4.2 TYPES OF HIGH PRESSURE VESSELS

High Pressure vessels are used as reactors, separators and heat exchangers. They are vessel with an integral bottom and a removable top head, and are generally provided with an inlet, heating and cooling system and also an agitator system. High Pressure vessels are used for a pressure range of 15 N/mm2 to a maximum of 300 N/mm2. These are essentially thick walled cylindrical vessels, ranging in size from small tubes to several meters diameter. Both the size of the vessel and the pressure involved will dictate the type of construction used.

A solid wall vessel consists of a single cylindrical shell, with closed ends. Due to high internal pressure and large thickness the shell is considered as a „thick‟ cylinder. In general, the physical criteria are governed by the ratio of diameter to wall thickness and the shell is designed as thick cylinder, if its wall thickness exceeds one-tenth of the inside diameter. A solid wall vessel is also termed as Mono Block pressure vessel.

18

2.4.3 TYPES OF FAILURES

 Elastic deformation—Elastic instability or elastic buckling, vessel geometry, and stiffness as well as properties of materials are protecting against buckling.  Brittle fracture—can occur at low or intermediate temperature. Brittle fractures have occurred in vessels made of low carbon steel in the 4050 F range during hydro test where minor flaws exist.  Excessive plastic deformation—the primary and secondary stress limits as outlined in ASME Section VIII, Division 2, are intended to prevent excessive plastic deformation and incremental collapse.  Stress rupture—Creep deformation as a result of fatigue or cyclic loading, i.e., progressive fracture. Creep is a time-dependent phenomenon, whereas fatigue is a cyclic-dependent phenomenon  Elastic instability—Incremental collapse; incremental collapse is cyclic strain accumulation or cumulative cyclic deformation. Cumulative damage leads to instability of vessel by plastic deformation.

 High Strain—Low cyclic fatigue is strain-governed and occurs mainly in lower strength/ high-ductile materials. 19

 Stress corrosion—it is well know that chlorides cause stress corrosion cracking in stainless steels; likewise caustic service can cause stress corrosion cracking in carbon steel. Materials selection is critical in these services.

 Corrosion fatigue—Occurs when corrosive and fatigue effects occur simultaneously. Corrosion can reduce fatigue life by pitting the surface and propagating cracks. Material selection and fatigue properties are the major considerations.

2.4.4 TYPES

 Thick Walled Pressure Vessels  Mono-bloc- Solid vessel wall.  Multilayer—Begins with a core about ½ in. thick and successive layers are applied. Each layer is vented (except the core) and welded individually with no overlapping welds. 

Multi-wall—Begins with a core about ½ in. to 2 in. thick. Outer layers about the same thickness are successive “shrunk fit” over the core. This 20

creates compressive stress in the core, which is relaxed during pressurization. The process of compressing layers is called autofrottage from the French word meaning self hooping.” Multilayer autofrettage Begins with a core about ½ in. thick. Bands or forged rings are slipped outside and then the core is expanded hydraulically.  The core is stressed into plastic range but below ultimate strength. The outer rings are maintained at a margin below yield strength. The elastic deformation residual in the outer bands induces compressive stress in the core, which is relaxed during pressurization. Wire wrapped vessels: Begin with inner core of thickness less than required for pressure. Core is wrapped with steel cables in tension until the desired auto frottage is achieved.  Coil wrapped vessels: Begin with a core that is subsequently wrapped or coiled with a thin steel sheet until the desired thickness is obtained. Only two longitudinal welds are used, one attaching the sheet to the core and the final closures weld. Vessels 5 to 6 ft in diameter for pressure up to 5000psi have been made in this manner.

21

2.4.5 THERMAL STRESS



Whenever the expansion or contraction that would occur normally as a result of heating or cooling an object is prevented, thermal stresses are developed. The stress is always caused by some form of mechanical restrain.

 Thermal stresses are “secondary stresses” because they are selflimiting. Thermal stresses will not cause failure by rupture. They can however, cause failure due to excessive deformations.

2.4.6 DISCONTINUITY STRESSES

Vessel sections of different thickness, material, diameter and change in directions would all have different displacements if allowed to expand freely. However, since they are connected in a continuous structure, they must deflect and rotate together. The stresses in the respective parts at or near the juncture are called discontinuity stresses. Discontinuity stresses are “secondary stresses” and are self-limiting. Discontinuity stresses do become an important factor in fatigue design where cyclic loading is a consideration. 22

2.5 FATIGUE ANALYSIS

When a vessel is subject to repeated loading that could cause failure by the development of a progressive fracture, the vessel is in cyclic service. Fatigue analysis can also be a result of thermal vibrations as well as other loadings. In fatigue service the localized stresses at abrupt changes in section, such as at ahead junction or nozzle opening, misalignment, defects in construction, and thermal gradients are the significant stresses.

2.5.1 STRESS

It is defined as the ratio of load into area is known as stress

23

2.5.2 TYPES OF STRESSES

1. Tensile

14. Compressive

2. Shear

15. Bending

3. Bearing

16. Axial

4. Discontinuity

17. Membrane

5. Tensile

18. Principal

6. Thermal

19. Tangential

7. Longitudinal

20. Load induced

8. Strain induced

21.

Circumferential

Longitudinal

Radial 9. Normal 10. Primary Stress 11. Primary general bending stress P b 12. Primary local stress, PL 13. Secondary stress:

24

2.5.3 PRIMARY GENERAL STRESS:

These stress act over a full cross section of the vessel. Primary stresses are generally due to internal or external pressure or produced by sustained external forces and moments. Primary general stress are divided into membrane and bending stresses. Calculated value of a primary bending stress may be allowed to go higher than that of a primary membrane stress. 1. Primary general membrane stress, Pm 2. Circumferential and longitudinal stress due to pressure. 3. Compressive and tensile axial stresses due to wind. 4. Longitudinal stress due to the bending of the horizontal vessel over the saddles. 5. Membrane stress in the centre of the flat head. 6. Membrane stress in the nozzle wall within the area of reinforcement due to pressure or external loads. 7. Axial compression due to weight. 8. Primary general bending stress, Pb Bending stress in the centre of a flat head or crown of a dished head. 9. Bending stress in a shallow conical head. 10. Bending stress in the ligaments of closely spaced openings. 25

2.5.4 PRESSURE STRESS:

The pressure stress limits may be discussed by considering a vessel that is constructed of a thin cylindrical shell of length L that is capped by a hemisphere at either end. The mean radius of the cylinder (and the caps) is denoted by R. The cylinder has a uniform thickness equal to tc; each cap has a uniform thickness equal to vessel is subjected to an internal pressure (p) and a zero external pressure. No other external forces act.

The vessel walls are at a uniform temperature and are

constructed of a single material.

2.5.5 SECONDARY STRESS:

 Secondary membrane stress Qm  Axial stress at the juncture of a flange and the hub of the flange  Thermal stresses.  Membrane stress in the knuckle area of the head.  Membrane stress due to local relenting loads  Secondary bending stress, Qb 26

 Bending stress at the gross structural discontinuity: nozzle, lugs, etc., (relenting loadings only).  The non uniform portion of the stress distribution in a thick-walled vessel due to internal pressure.  The stress variation of the radial stress due to internal pressure in thick-walled vessels.  Thermal stress in a wall caused by a sudden change in the surface temperature.  Thermal stresses in cladding or weld overlay.

2.6 FAILURE IN PRESSURE VESSELS

Categories of Failures:  Material--Improper Selection of materials; defects in material.  Design—Incorrect design data; inaccurate or incorrect design methods; inadequate shop testing.  Fabrication – Poor quality control; improper or insufficient fabrication procedures including welding; heat treatment or forming methods.

27

 Service—Change

of

service

condition

by

the

user;

inexperienced operations or maintenance personnel; upset conditions. Some types of services which requires special attention both for

election of materials, design details, and

fabrication methods are as follows: 1. Lethal

6. Fatigue (cyclic)

2. Brittle (low temperature)

7. High

Temperature 3. High shock or vibration

8. Vessel contents

4. Hydrogen

9. Ammonia

5. Compressed air

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CHAPTER: 3

CODES AND STANDARDS

The following codes and standards shall be followed unless otherwise specified:

ASME SEC. VIII DIV.

For Pressure vessels

IS: 2825 ASME SEC. VIII DIV.2

For Pressure vessels (Selectively for high Pressure / high thickness / critical service)

ASME SEC. VIII DIV.2

for Storage Spheres

ASME SEC. VIII DIV.3

For Pressure vessels (Selectively for high

API 650 / IS: 803

pressure)

API 620

For Storage Tanks.

API 620 / BS 7777

For Low Pressure Storage Tanks,

ASME SEC. VIIIDIV.1

Cryogenic Storage Tanks (Double Wall) For workmanship of Vessels not categorized under any other code.

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CASE 1: MATERIALS OF CONSTRUCTION

YP (Min) UTS (Min) Description

Material

Type of Steel

N/mm2 N/mm2

SA 515 GR Shell Liner

267.6 Austenitic

492.9

70 Shell Layers

SA 212 GR B

Carbon Steel

490.0

SA 515 GR Dished Ends

267.6 Austenitic

492.9

70

30

MATERIAL PROPERTY SUMMERY

Material

Density(g/cm3)

Tensile

Tensile

strength(Mpa)

Modulus(Mpa)

Aluminum(6061 t6)

310

69

2.71

Steel(SAE4340)

1034

200

7.83

Boron Fiber

3516

300

2.57

Carbon Fiber(p-55)

1724

379

1.99

Gr 33 150 gsm/BT 250

1965

13100

1.55

31

3.1

MATERIAL

SELECTION

FOR

PRESSURE

VESSEL

CONSTRUCTION

Materials are generally selected by the user for whole of the plant and specifically, by pressure vessel designer/ supplier according to the following criteria.  Corrosive or noncorrosive service  Contents and its special chemical/physical effects  Design condition (temperature)  Design life and fatigue affected events during the plant life  Referenced codes and standards  Low temperature service  Wear and abrasion resistance  Welding and other fabrication processes

32

3.2 GENERAL MATERIAL SELECTION PROCESS

The objective is to select the material which will most economically fulfill the process requirements. The best source of data is well-documented experience in an identical process unit. In the absence of such data, other data sources such as experience in pilot units, corrosion coupon tests in pilot or bench-scale units, laboratory corrosion-coupon tests in actual process fluids, or corrosion- coupon tests in synthetic solutions must be used. Permissible corrosion rates are an important factor and differ with equipment. Appreciable corrosion can be permitted for tanks and lines if anticipated and allowed for in design thickness, but essentially no corrosion can be permitted in fine-mesh wire screens, orifices, and other items in which small changes in dimensions are critical. In many instances use of nonmetallic materials will prove to be attractive from an economic and performance standpoint. These should be considered when their strength, temperature, and design limitations are satisfactory. In the selection of materials of construction for a particular fluid system, it is important first to take into consideration the characteristics of the system, giving special attention to all factors that may influence corrosion. Since

33

these factors would be peculiar to a particular system, it is impractical to attempt to offer a set of hard and fast rules that would cover all situations. The materials from which the system is to be fabricated are the second important consideration; there

3.3 MATERIALS USED FOR PRESSURE VESSELS Most of pressure vessels used in the petrochemical equipment is made of steel. The manufacturing materials are varied, and the commonly used materials are as follows. 1. Q235-A With more silicon content and complete deoxidization, Q235-A has better quality. The limited range of application: the design pressure is less than or equal to 1.0MPa, the design temperature is between 0 and 350℃, and the thickness of steel plate cannot be more than 16mm when Q235-A is used to manufacture the shell. Q235-A cannot be used to manufacture the pressure vessel which is filled with liquefied petroleum gas and the medium with its extreme toxicity degree and high harm, and is heated directly by flame.

34

2. 20g

20g boiler steel plate is the same as the common 20 high-quality steel. Compared with Q235-A, 20g boiler steel plate has lower sulfur content and higher strength, and the range of its service temperature is from -20 to 475℃. Therefore, 20g is often used to manufacture the medium pressure vessels with higher temperature.

3. 16MnR

16MnR common low alloy vessel steel plate is used to manufacture medium, low pressure vessels, which can reduce the weight of the vessel with higher temperature. Besides, the range of its service temperature is from -20 to 475℃.

35

4. THE MATERIAL FOR LOW TEMPERATURE VESSELS (LESS THAN -20℃)

This kind of material is mainly required to have better toughness to prevent the brittle rupture at low temperature. Generally the steel for low temperature vessel mostly adopts manganese vanadium steel.

3.4 STEEL FOR HIGH TEMPERATURE VESSELS

When the temperature is less than 400℃, the common carbon steel can be adopted; when the service temperature is between 400 to 500℃, 15MnVR and 14MnMoVg can be adopted; when the service temperature is between 500 to 600℃, 15CrMo and 12Cr2Mol are adopted; when the service temperature is from 600 to 700℃, such high alloy steels as 0Cr13Ni9 and 1Cr18ni9Ti should be adopted.

36

CHAPTER 4

DESIGN OF MULTILAYER HIGH PRESSURE VESSEL

Multi layer vessels are built up by wrapping a series of sheets over a core tube. The construction involves the use of several layers of material, usually for the purpose of quality control and optimum properties. Multi layer construction is used for higher pressures. It provides inbuilt safety, utilizes material economically, no stress relief is required. For corrosive applications the inner liner is made of special material and is not considered for strength criteria. The outer load bearing shells can be made of high tensile low carbon alloys.

37

4.1 DESIGN OBJECTIVES

1. To show that multilayer pressure vessels are suitable for high operating pressures than solid wall pressure vessels. 2. To show a significant saving in weight of material may be made by use of a multilayer vessel in place of a solid wall vessel. 3. To show there may be a uniform stress distribution over the entire shell, which is the indication for most effective use of the material in the shell. 4. To check the suitability of using different materials for Liner shell and remaining layers for reducing the cost of the construction of the vessel. 5. To verify the theoretical stress distribution caused by internal pressure at outside surface of the shell and to ascertain that the stresses do not reach yield point value during testing. 6. Finally check the design parameters with FEM analysis by using ANSYS package to ascertain that FEM analysis is suitable for multilayer pressure vessel’s analysis.

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4.2 DESIGN CONSIDERATIONS

1. A multilayer Vessel is designed to ASME Code Section VIII division I. 2. A Safety Factor of “3” on Ultimate Tensile Strength is considered in the design of the multi layer shell only. For other parts the Factor of Safety is taken as “4” at room temperature. 3. A joint efficiency of 100% for longitudinal seam on liner shell is taken. 4. 100% radiography for longitudinal seam of liner shell. 5. Fully ultrasonic test for dished end plates is considered. 6. Dished ends to be stress relieved after attachment of boss, nozzle etc., 7. The longitudinal welds in a multilayered shell were staggered. 8. The number segments (longitudinal welds) in a layer are taken as “3”. 9. The coefficient of weld shrinkage is taken as 10%.(From Davis R.L, “Circumferential welds in Multilayer Pressure Vessel” Paper .70WA/PVP-6.) 10. The thickness of the liner shell is taken as 12 mm. 11. The thickness of subsequent layers is 6 mm.

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4.3 DESIGN DATA OF THE VESSEL:

Design Pressure P - 21 N/mm2, Hydrogen. Design Temperature, T - 200C Hydrostatic Pressure PH - 27.3 N/mm2 Drawing of Multilayer Pressure Vessel

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4.4 DESIGN CRITERIA 4.4.1 MINIMUM SHELL/HEAD THICKNESS

Minimum thickness shall be as given below a) For carbon and low alloy steel vessels- 6mm (Including corrosion allowance not exceeding 3.0mm), but not less than that calculated as per following: FOR DIAMETERS LESS THAN 2400mm Wall thickness = Dia/1000 +1.5 + Corrosion Allowance

FOR DIAMETERS 2400mm AND ABOVE Wall thickness = Dia/1000 +2.5 + Corrosion Allowance All dimensions are in mm. b) For stainless steel vessel and high alloy vessels -3 mm, but not less than that calculated as per following for diameter more than 1500mm. Wall thickness (mm) = Dia/1000 + 2.5 Corrosion Allowance, if any shall be added to minimum thickness.

41

c) Tangent to Tangent height (H) to Diameter (D) ratio (H/D) greater than 5 shall be considered as column and designed accordingly. d) For carbon and low alloy steel columns / towers -8mm (including corrosion allowance not exceeding 3.0mm. e) For stainless steel and high alloy columns / towers -5mm. Corrosion allowance, if any, shall be added to minimum thickness.

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CHAPTER: 5 FACTORS CONSIDERED FOR DESIGNING PRESSURE VESSEL

5.1 VESSEL SIZING

 All Columns based on inside diameter  All Clad/Lined Vessels Based on inside diameter  Vessels (Thickness>50mm) Based on inside diameter  All Other Vessels based on outside diameter  Tanks & Spheres based on inside diameter

5.2 VESSEL END CLOSURES:

1. Unless otherwise specified Deep Torispherical Dished End or 2:1 Ellipsoidal Dished 2. End as per IS - 4049 shall be used for pressure vessels. Seamless dished end shall be used for specific services whenever specified by process licensor. 43

3. Hemispherical Ends shall be considered when the thickness of shell exceeds 70mm. 4. Flat Covers may be used for atmospheric vessels 5. Pipe Caps may be used for vessels diameter < 600mm having no internals. 6. Flanged Covers shall be used for Vessels /Columns of Diameter < 900mm having Internals. 7. All columns below 900mm shall be provided with intermediate body flanges. Numbers of Intermediate flanges shall be decided based on column height and type of internals 5.3 PRESSURE

Pressure for each vessel shall be specified in the following manner:

5.3.1 OPERATING PRESSURE

Maximum pressure likely to occur any time during the lifetime of the vessel

44

5.3.2 DESIGN PRESSURE

When operating pressure is up to 70 Kg./cm2 g , Design pressure shall be equal to operating pressure plus 10% ( minimum 1Kg./cm2 g ).r all the three cases, Allowable Stress values: Shell Liner & Layers ; 164 N/mm2 Dished Ends : 123 N/mm2

5.3.3 TEST PRESSURE

a) Pressure Vessels shall be hydrostatically tested in the fabricators shop to 1.5 /1.3/ 1.25 (depending on design code) times the design pressure corrected for temperature. b) In addition, all vertical vessels / columns shall be designed so as to permit site testing of the vessel at a pressure of 1.5/ 1.3 / 1.25 (depending on design code) times the design pressure measured at the top with the vessel in the 45

vertical position and completely filled with water. The design shall be based on fully corroded condition. c) Vessels open to atmosphere shall be tested by filling with water to the top. d) 1.Pressure Chambers of combination units that have been designed to operate independently shall be hydrostatically tested to code test pressure as separate vessels i.e. each chamber shall be tested without pressure in the adjacent chamber. 2. When pressure chambers of combination units have their common elements designed for maximum differential pressure the common elements shall be subjected to 1.5/ 1.3 times the differential pressure.

3. Coils shall be tested separately to code test pressure. e) Unless otherwise specified in applicable design code allowable stress during hydro testing tension shall not exceed 90% of yield point. f) Storage tanks shall be tested as per applicable code and specifications.

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5.3.4 CORROSION ALLOWANCE:

Unless otherwise specified by Process Licensor, minimum corrosion allowance shall be considered as follows: - Carbon Steel, low alloy steel column, Vessels, Spheres : 1.5 mm - Clad / Lined vessel: Nil - Storage Tank, shell and bottom: 1.5 mm - Storage tank, fixed roof / Floating Roof: Nil For alloy lined or clad vessels, no corrosion allowance is required on the base metal. The cladding or lining material (in no case less than 1.5 mm thickness) shall be considered for corrosion allowance. Cladding or lining thickness shall not be included in strength calculations. Corrosion allowance for flange faces of Girth / Body flanges shall be considered equal to that specified for vessel.

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5.5.5 CALCULATION

Dynamic analysis of each column shall be carried out for stability under transverse wind induced vibrations as per standard design practice. The recommended magnification amplitude shall be limited to tower diameter divided by five.

5.6 DESIGN PROCEDURE AND CALUCULATION: 5.6.1 CIRCUMFERENTIAL OR HOOP STRESS: Tensile stress acting in a direction tangential to the circumference is called

Circumferential or Hoop Stress. In other words, it is on longitudinal section (or on the cylinder walls).

Let, p = Intensity of internal pressure, d = diameter of the cylinder shell l = length of cylinder, t = Thickness of the shell, and σ t1= hoop stress for the material of the cylinder. Now, we know that

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Total force on a longitudinal section of the shell = Intensity of pressure × projected Area = px d × l ………….….. (1) and the total resisting force acting on the cylinder walls=σ

t1×

2t ×

l...…(2) From equation (1) and (2), we have σ× 2t × l = p × d × l or σ t1x2txl= p d l (or) σ t1 =pd/2t 5.6.2 LONGITUDINAL STRESS:

Tensile stress acting in a direction of the axis is called longitudinal stress. In other words, it is tensile stress acting on the transverse or circumferential section. Let σ t2= Longitudinal stress. In this case, total force acting on the transverse section= Intensity of pressure × Crosssectional Area = p ×4π (d) ² ………(i) and Total resisting force

= σ t2×d.t ……ii 49

From equation (i) and (ii), we have σ t2×πd.t = p ×4 π (d) ² σ t2x4txl= p d l

(or) σ t2 =pd/4t

5.7.1 DESIGN OF SHELL DUE TO INTERNAL PRESSURE:

As discussed in article on thin vessel are cylindrical pressure vessel is subjected to tangential (σ t) and longitudinal (σ l) stresses. σ t=Pi x Di/2t σ l=Pi xDi /4t Where D= mean diameter D=Di + t 5.7.2 RULE:

The design pressure is taken as 5% to 10% more than internal pressure, where as the test pressure is taken as 30% more than internal pressure. Considering the joint efficiency, The thickness of shell can be found by following procedure, η ×σ =Pi×(Di+t)/2t η ×σ x2t =Pi×(Di+t) 50

5.7.3 DESIGN OF ELLIPTICAL HEAD: Elliptical heads are suitable for cylinders subjected to pressures over 1.5 MPa. The shallow forming reduces manufacturing cost. It’s thickness can be calculated by the following equation: t = pi di W/2σ J Where, di = Major axis of ellipse W= Stress intensification factor W= 1/6 (2+K2) Where k = Major Axis Diameter/Major Axis Diameter

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5.8 DESIGN CALCULATION:

5.8.1 THICKNESS OF CYLINDER:

Given data Internal pressure (P) = 0.588 MPa Internal Diameter (Di) = 496mm Corrosion Allowance (CA) = Nil. Joint Efficiency for shell = 1. t=(Pi xDi /2 xσ x η –Pi)x CA

( CA is NIL)

= 1.066 ∴ t = 1.066mm

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5.8.2 DESIGN OF MANHOLE:

GIVEN DATA: Internal pressure (Pi) = 0.588 N/mm2 Internal diameter (Di) = 496 mm Thickness (t) = 6 mm. CA = NIL Joint Efficiency (η) = 1 Internal diameter of nozzle (di) = 254.51 mm d = d i + CA = 254.51 mm. tr = require thickness = 1.066 mm. tn = Actual thickness of nozzle = 9.27 mm. trn = Required thickness as per calculation in mm. A1= 0.588 x 254.51/ 2 137 x 1 0.588 tm=P i D i /2 σ η –Pi ttm= 0.588 x254.51/ 2 137 x1 0.588 t m=1.66mm

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5.8.3 DESIGN CALCULATION SUMMARY:

SHELL

INTERNAL

496mm

DIAMETER (DI) THICKNESS

6mm

(T)

HEAD

THICKNESS

6mm

(T)

HEIGHT (H)

173mm

THICKNESS

9.27mm

OF NOZZLE (TN)

CYLINDER

THICKNESS

1.6mm

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ADVANTAGES

 Home application.  Industrial application.

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CONCLUSION This project work has provided us an excellent opportunity and experience, to use our limited knowledge. We gained a lot of practical knowledge regarding, planning, purchasing, assembling and machining while doing this project work. We feel that the project work is a good solution to bridge the gates between institution and industries. We are proud that we have completed the work with the limited time successfully. It is working with satisfactory conditions. We are able to understand the difficulties in maintaining the tolerances and also quality. We have done to our ability and skill making maximum use of available facilities. In conclusion remarks of our project work, let us add a few more lines about our impression project work. By using more techniques, they can be modified and developed according to the applications.

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REFERENCES

1. Matthews, Clifford. Engineers’ Guide to Pressure Equipment. London: Professional Engineering Publishing, 2001.

2. Chattopadhyay, Somnath. Pressure Vessel Design and Practice. s.l. : CRC Press, 2005.

3. Carruci, Vincent A. Overview of Pressure Vessel Design. s.l. : ASME International, 1999. 4. ASME, the American Society of Mechanical Engineers. Rules for Construction of Pressure Vessels (Sec. VIII, Division 1). ASME Boiler and Pressure Vessel Code. New York: ASME (The American Society of Mechanical Engineers), 2007.

5. Ellenberger, J. Phillip, Chuse, Robert and Carson, Bryce E. Pressure Vessels: The ASME Code Simplified. 8th Edition. s.l.: McGraw-Hill, 2004.

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6. Bringas, John E. The Metals Black Book. Edmonton, Alberta: CASTI Publishing Inc, 1995.

7. Moen, Richard A. Practical Guidebook Series™ ASME Section II 1997 Materials Index. Edmonton, Alberta: CASTI Publishing Inc., 1996.

8. Perry, R. H., and Chilton, C. H. Perry’s Chemical Engineer’s Handbook, 5th ed. New York: McGraw-Hill, 1973.

9. White, R. A. and Ehauke, E. F. Materials Selection for Refineries and Associated Facilities. San Francisco, California:

10. Bednar, Henry H. Pressure Vessel Design Handbook. 2nd Edition. Malabar, Florida: Krieger Publishing Company, 1986.

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